The present invention relates to a method and an apparatus for the manufacture of non-allergenic creating objects of precious metals. By precious metal objects are meant any type of objects which are completely or partly made of a precious metal or a precious metal alloy, and the invention is especially concerned with such objects which are supposed to get in contact with the skin of a human body, for instance finger rings, bracelets, jewel chains, brooches, amulets, earrings, watches, glasses and sun-glasses etc. The precious metal may be gold, silver, platina, rodium, palladium and other precious metals suited for the manufacture of the above mentioned objects. The precious metals may be solid or may be in the form of double or any other surface covering of some less precious metal like copper, zinc, aluminum, tin or chrome or nickel or any alloy of such metals. According to the invention the object also may be made as a whole of these non-precious metals.
It is known that many people are hit by different kinds of illness conditions at skin contact with jewels, watches, glasses and many other objects made of the said metals. Special troublesome phenomena may appear when the said objects get in contact with very thin skin with high transmittance get in contact with very thin skin with high transmittance ability like for instance rings, especially earrings applied through holes in the ear tip. The illness conditions generally are skin troubles like itching, scorching, eryphema, exanthena, liquid containing blisters or suppuration boils. In addition to such skin troubles more intense illness conditions may appear.
Test have proven that the said illness conditions which generally are referred to as allergic affections do not appear if the object in contact with the human skin is made of optimum pure and clean metals of gold, silver, platinum (platina), rodium, palladium etc. not even if the said metals have been alloyed with optimum pure and clean copper, zinc or tin or even aluminum, nickel or chrome. There are reasons to believe that the said allergic affections depend on impurities in the metal or the metal alloys. It may be assumed that some alloy substances cause serious allergic affections, like for instance alloyed heavy metal like cadmium, lead, mercury, bismuth, antimony, cobalt, etc. Allergic affections also may appear if impure alloy metals are used like impure copper, zinc, tin or any other impure alloy metals. Impurities may appear both when manufacturing the precious metal or the precious metal alloy itself or during the working and the following treatment of the metal of the metal alloy. For instance impurities may be added in the precious metal, the alloy metal or the alloy if treated with an acid during the manufacture or the subsequent treatment. Copper has a great tendency of assimilating many different types of impurities. Without the risk of the appearance of allergic problems, optimum pure and clean copper, optimum pure zinc, optimum pure tin and possibly even optimum pure aluminum, chrome or nickel and other metals may be used as alloy metals. On the contrary it is of great importance that most types of heavy metals and thereby related or similar metals like cadmium, lead, mercury, bismuth, antimony, cobalt etc. are completely excluded from the alloy.
It is also of importance to eliminate the impurities and any further metals or any other allergy creating substances in the base metal of objects covered with precious metals, so called double objects or objects coated in any other way. All metals are more or less "leaky", and by metal transient movements heavy metals and impurities and other allergy creating substances in the base of a double object or an object coated in any other way may be released from said base and may move through the precious metal layer and dispose as a surface covering of the object. By the invention it has also been shown that, for instance, cadmium has a great tendency for such metal transient movement. Cadmium alloyed objects therefore generally get a more or less thin surface covering of the allergy creating heavy metal cadmium.
In the manufacture of objects of non-alloyed precious metals or precious metals alloyed with optimum pure alloy metals like copper, zinc, tin and even chrome or nickel, there often arise manufacturing technical problems.
As an example, silver in combination with copper has a so-called shape memory, and as a consequence when heat treating a cold worked silver object the object tends to regain the form that the silver object had before the cold working. Such shape memory causes large problems for instance when soldering the objects in that the joint opens when the objects is heated and there is a risk of bad soldering. In order to neutralize the shape memory of the silver and to make the silver shape willing, cadmium generally is added to the silver. Often an addition of more than 7% cadmium was needed in order to obtain the intended effect. When adding cadmium to the silver, a brittle soldering joint is obtained. An addition of cadmium in a silver alloy however, gives serious allergy problems. Equivalent problems appear when manufacturing objects of gold, platinum (platina), palladium, rodium and other precious metals as well as when manufacturing objects of copper, zinc, aluminum, tin and even nickel or chrome or alloys like brass or tombak.
When performing stress-relieving annealing, salts generally are used, so-called hardening salts. The salts may be hot or cold. For the purpose of cooling the metals in connection to stress-relieving annealing, water mixed with certain salts often is used for raising the evaporating temperature. Also, such salts may cause allergic affections, and it is also important to forsee that the metal object does not get in contact with such salts.